Cell surface glycans are major determinants of cell-cell and cell-matrix interactions. Changes in cell surface glycosylation mark the onset of cancer and inflammation. Inside the cell, they can regulate transcription, translation as well as protein trafficking. Progress toward delineating the molecular basis of glycan function, however, has been rather slow. This is partly due to the fact that the biosynthesis of glycans, unlike other biopolymers, is neither template-driven nor under direct transcriptional control. Therefore, conventional genetic and biochemical approaches for elucidating glycan function, and its relevance to disease, have yielded limited information. The long-term goal of this project is to implement click chemistry--a set of powerful, reliable and selective reactions--as a general tool for fundamental studies of glycobiology. [unreadable] [unreadable] The major objective of the first granting period (K99) is to initiate steps for applying click chemistry in studies of protein glycosylation in the lab of Professor Carolyn Bertozzi (the mentor). Aim 1 intends to use click chemistry-based bioorthogonal reactions to prepare homogeneous glycoproteins with therapeutic value. A genetically encoded aldehyde tag will be used for site-specific glycosylation. Aim 2 is to design and build specific lectin and antibody sensors using glycodendrimer-functionalized carbon nanotubes. [unreadable] [unreadable] With the experience and knowledge gained from the research in the first granting period, I will expand the applications of click chemistry in two new directions in the next granting period (R00). Aim 3 is to discover/ develop small molecule inhibitors of glycan biosynthetic and processing enzymes using enzyme-templated in situ click chemistry. For proof of principle, I chose O-beta-N-acetylglucosaminyl-transferase (OGT) as the first target. I plan to develop fragment libraries that will be screened for self-assembled inhibitors of OGT. Given the correlation of excessive O-GlcNAc modification with insulin resistance-triggered hyperglycemia, the compounds developed may have applications in diabetes therapy. Aim 4 is to intercept glycan biosynthetic pathways with synthetic unnatural substrates bearing bioorthogonal functional groups, such as azides and alkynes. In parallel, I will also develop new selective reactions based on click chemistry for their subsequent detection in live cells. [unreadable] [unreadable] Glycans are known to participate in many normal and disease processes. This series of experiments will advance our understanding of glycan biosynthesis and carbohydrate-protein interactions related to these disease states. These studies may also offer new avenues for therapeutic intervention. I anticipate that the new chemical tools developed in these studies will have broad applications in biomedical research. [unreadable] [unreadable] [unreadable]